Ceteris paribus is the Latin phrase meaning “all other things being equal” or “with other conditions held constant.”
Scientists and researchers use the phrase when they want to isolate the effect of one variable. For example, an experiment might ask whether increasing fertilizer changes plant growth, ceteris paribus—in other words, while keeping factors such as soil, water, light, and temperature as similar as possible. This helps make comparisons and causal reasoning more manageable.
The phrase does not claim that every other factor literally remains unchanged in the real world. It identifies a simplifying assumption or an experimental goal. In complex systems, unmeasured influences may still affect the result, which is why controlled experiments, randomization, replication, and statistical analysis matter.
Ceteris paribus is also common in economics. A statement about demand may examine the effect of price while assuming income, tastes, prices of related goods, and other influences remain constant. The phrase is not the same as a priori, which means independent of experience, or post hoc, which refers to reasoning after an event.